Working aluminous metals



J 31, 1967 T. L. FRITZLEN ET AL 3,301,029-

WORKING ALUMINOUS METALS Filed July 6, 1964 IN VENTORS THOMAS L.FRITZLEN LJNTON D. BYLUND ATTORNEYS United This invention relates to the production of highly finished metal sheets, plates and strips and is especially directed to a novel process for the rolling of aluminum and aluminum-based alloys (hereinafter referred to as aluminum alloys) so as to obtain products which are distinctly superior to those heretofore obtained. More particularly, this invention is directed towards a novel process for the hot rolling of aluminum alloys so as to obtain products of improved surface finishes, i.e., having a smoother surface and a higher degree of brightness, such that they are particularly adapted to be employed in those areas wherein the appearance of the finished article is of extreme importance, or where a smooth surface of the rolled sheet is more amenable to subsequent operations such as, drawing, forming, brightening, or anodizing.

The rolling of aluminum alloys to produce metal sheet and plate is a widely practiced commercial operation and various proposals have heretofore been suggested to improve the quality of the hot rolled surface. Thus, common problems which are encountered in the hot rolling and subsequent cold rolling of metals and, in particular aluminum alloys, would include thickness irregularities, camber, waves or the like, scratching, dullness, oxide pickup, roughness, minute broken surface, rolled-in or rolledover carbonaceous products and other impairment of the metal surface, as well as impairment of the surface of the rolls themselves during prolonged operation. In an attempt to overcome these difiiculties, the prior art has resorted to spraying or otherwise placing a lubricating oil, either by itself or in the form of an aqueous emulsion or solution in contact with the metal rolls so as to improve the quality of the rolled product. Although the use of a lubricating oil has, in fact, resulted in an improvement, not only in the etficiency of the rolling process, but also in the surface of the resulting products, nevertheless the products which were directly obtained from the rolling mill did not have consistent quality with respect to the surface to be used in those areas wherein the appearance or smoothness of the article is of utmost importance.

Accordingly, it is the primary object of this invention to provide a novel process for the rolling of aluminum alloys so as to produce products with a more uniform and smoother surface with improved brightness.

It is another object of this invention to provide a novel process for the hot rolling of aluminum alloys which is capable of yielding a product of improved surface characteristics, so that an extremely bright surface can be obtained by chemical brightening or electropolishing when followed by anodizing.

Other objects, purposes and advantages of the invention will become obvious from the ensuing description thereof.

It has now been discovered that products having improved surface characteristics will result from carrying out the rolling of aluminum alloys with a rolling oil or an emulsion of a rolling oil and water, to which has been added an inert gas. While not wishing to be bound by any theory of operation due to the fact that many factors must be taken into consideration in attempting to explain the surface characteristics of metals, it nevertheless appears that when an aluminum alloy passes through a roll- Patent 0 "ice ing mill a fresh surface is produced which can react with the oxygen in the air to produce aluminum oxide in varying degrees so as to result in surface blemishes. The novel process of this invention provides an inert atmosphere in the area of the rolling mill, coupled with a lowoxygen-content soluble oil mixture, so that the freshly formed aluminum surface cannot react with the atmosphere thereby obtaining products having improved surface characteristics. As can well be appreciated, the tendency of aluminum or aluminum alloys to oxidize in air can generally be said to be directly proportional to temperature. Therefore, since the aluminum alloy in passing through the rolling mill is at a relatively high temperature due to the fact that it has not yet been sufficiently cooled by the mixture of oil and water, the provision of an inert atmosphere and relatively oxygen-free soluble oil solution at this point greatly reduces rapid and uneven oxide formation so that the resulting product possesses a high degree of brightness with a smoother surface and with the production of less detritus to accumulate in the soluble oil solution.

Detritus is defined in this case as the material wearing away from the surface of the aluminum slab and the surfaces of the steel rolls making contact with it while the slab is between the rolls.

The expression inert atmosphere or inert gas as used throughout the specification and claims is intended to mean substances which will not react with aluminum or aluminum alloys at the temperatures attained during hot rolling, or cold rolling. In this connection it is well to consider that carbon dioxide could not be used, since this gas was found to react with the freshly rolled aluminum surface to produce excessive and uneven oxide formation. Suitable inert materials which are operable would include nitrogen, helium, hydrogen, neon, argon, and krypton, although nitrogen is preferred for obvious economic considerations.

The process of this invention is carried out simply by bubbling a suitable inert gas, i.e., nitrogen, through a rolling oil or a mixture of a rolling oil and water, and then spraying the resulting composition and mixture of soluble oil solution and nitrogen gas onto a rolling mill.

A particular advantage of the novel process of this invention resides in its use in the hot rolling of aluminum alloys since it is believed that the surface of the aluminum alloy undergoing deformation will be torn, fractured, or sheared whenever the temperature of the surface of the metal being deformed attains a value where the tensile strength and shear strength is insufficient to withstand the stresses imposed. Furthermore, it is known that in hot rolling the aluminum alloy is deformed to an extent to elongate from 4 to 60 percent, depending on the hardness of the particular aluminum alloy being hot rolled, the thickness of the ingot or slab to be reduced, and the type of mill used, thereby exposing a fresh surface to be oxidized. The ingot temperature ranges from about 800 F. to 1000 F., depending on the alloy being hot rolled, while the finished slab temperature ranges from about 400 F. to 500 F., dependent on the aluminum alloy being hot rolled and the thickness attained. The oxidation of aluminum is exothermic, thereby heating the asperities upon the surface of the aluminum and the asperities upon the surface of the steel roll when in contact with air (oxygen) or the oxygen contained in the soluble oil solution being used. This exothermic oxidation is inhibited by this invention of introducing nitrogen gas with the soluble oil solution during hot rolling of aluminum and its alloys in a single stand, or multiple stand mill, thereby improving the surface of the resulting aluminum slab with respect to fractures, broken surface, oxide pickup, and a generally roughened surface. It is also believed that the detritus is increased by the exothermic oxidation of the aluminum and steel surfaces (asperities) which are torn loose or ground off in the hot rolling operation.

is attached to a suitable source of inert gas (not shown) delivers said gas to the tank containing the rolling oil and to the suction side of the pump 8. The flow rate of the gas is not narrowly critical but it is preferred to use It is known that air, nitrogen and oxygen are soluble from about 5 to about 3000, and more preferably from in water to some extent, and that the solubility decreases to 100 cubic feet per hour at S.T.P. per 2400 cu. ft./hr. with increasing temperature. The following analyses of rolling oil or emulsion or rolling oil which is to be made on soluble oil solutions for nitrogen and oxygen treated. It is understood that it is not absolutely necesshow the effect of purging the aqueous solutions with sary for the inert gas to enter directly into the tank connitrogen gas, and also the effect of use in hot rolling 1O taining the rolling oil and water, but said gas could also aluminum alloys when introduced through the spray sysbe introduced into the outlet side of pump 8 or directly tern with somewhat less than 2 /2 percent by volume of into pipes 10 and 11. nitrogen gas to cool the slab, or ingot, and the steel rolls Rolling oils which are operable in the novel process of during hot rolling. this invention are well known in the art and would in- Nitrogen Gas Volume, ml. per 1 Soluble Oil Solution Nitrogen Used in Liter Ratio Concentration, percent lurged Rolling O /N,

Oxygen Nitrogen The method of analysis used is believed to be accurate clude palm oil, cocoanut oil, lard, other fatty acids, and to within 10 percent. It can be seen that the oxygen relatively high-boiling hydrocarbons, including synthetic content of the soluble oil solution was decreased by purgand/or mineral oils, together with conventional additives ing with nitrogen gas, and was decreased to a greater exsuch as emulsion, etc., used as lubricants in metal fabritent with the particular soluble oil solution having at cation and deformation processes. As has heretofore leasta2 /2 percent concentration. been pointed out, the rolling oil is preferably used in Referring to the figure the apparatus there shown comadmixture with water and suitable aqueous mixtures can prises a pair of mating rolls 1 and 2 of a rolling mill contain from 1 to 50 percent by weight and more preferwhich act upon a sheet, strip, or bar of aluminum or ably 2 to 12 percent by weight of the rolling oil. The aluminum alloy 3 to reduce its thickness as indicated at 4, particularly preferred rolling oils are those commonly a plurality of rows of spray nozzles 5 being provided for referred to in the art as soluble oils. As is well known applying the treated aqueous oil emulsion to each side in the art, soluble oils are marketed under various proof each roll and to each side of the strip before, during prietary names, such as Prosol (Socony Mobil Oil Co., and after rolling. A suitable trough or pit 6 may be Inc.), Texaco C (Texas Company), and these oils are provided for receiving or collecting the oil after passing obviously operable in the novel process of this invention. over the rolls 1 and 2 and the metal strip portions 3 and The following example will illustrate the novel process 4, this coolant being delivered to a suitable receiving of this invention. tank 7. The rolling oil is withdrawn from the tank 7 EXAMPLE 1 by Sultable cenmfugfl pump 8 and 15 passed thl-noug-h An aluminum alloy ingot containing 99.5 percent alua pipe 9 to the two pipes 10 and 11 each of wh1ch 1s mmum was passed through a 3-h1gh reversing hot rolllng shown as provided with two rows or sets of spray nozzles 5 one row or set bein above the aluminum stri and the mln usmg 24 dlameter 56 wlde rolls at a rate of other below p proximately 75 feet per minute. At both the inlet and It will be noted that the position of manifold 11 and Outlet. Sides of the was sprayed i t contammg 12 percent by weight of Texaco C rolling the nozzles 5 (entry) is such that both the upper and 011, a product of the Texas Company, into which nitrogen lower surfaces of the entry slab and the top and bottom gas was continuously bubbled during hot rolling at the entry roll surfaces of rolls 1 and 2 are sprayed, cooled, l

. rate of cubic feet per hour. The nitrogen gas outlet lubricated and provided w1th an 1nert atmosphere blanket was placed underneath the suction end of the soluble 011 as the rolling process proceeds. That is, the top and suction p1pe leading to the rolling mill. Hence, the nitrobottom entry nip angle are flooded with the nitrogenated (mated Soluble oil emulsion W 8 fed t th e t a d soluble rolling emulsion-nitrogen gas mixture during roll- 60 i the min via the coolin g 1 n ing. The spray nozzles 5 (exit) associated with the other g an u 9 1 y $31.5 Fourteen cells were rolled, each coil having a brighter manifold 10 are located so that the exitmg side of rolls Surface No build 0 i k f th et 1 th 1 and 2 are sprayed in such a manner that an inert rolls 1 noticed up I p c 0 e m a on 6 atmosphere is provided at both the upper and lower sur- EXAMPLE 2 faces of exit strip 4 after being reduced in thickness; that is, the exit nip angles, top and bottom, are also The procedure of Example 1 was repeated with the blanketed with the nitrogenated -N gas mixture. It exception that no nitrogen was bubbled through the rollwill be understood that other types of mills, such as 3- ing oil. Fourteen coils were rolled and the surfaces were high, 4-high, multi-stand mills, etc., may be employed if dull and had considerable surface tearing, and oxide pickdesired in accordance with conventional practice. Moreup of the metal on the rolls was noticed. over, if desired, only two sets of spray nozzles such as Many variations of the above examples will occur to those shown on pipe 10 (the exit side) may be used those skilled in the art and this invention is not intended although it is to be understood the optimum results are to be limited except as necessitated by the appended obtained when the treated rolling oil is sprayed on both claims. Thus, for example, although the process of this the inlet and outlet side of the mill. Inlet pipe 12 which invention has been described with reference to the hot rolling of aluminum alloys, it is to be understood that other processes for the high temperature working of aluminum alloys, such as forging and drawing processes and impact extrusion processes, are to be included within the scope of this invention. Additionally, although the provision of an inert atmosphere has been described by bubbling an inert gas through a tank containing a rolling oil, an emulsion thereof, and also into the soluble oil itself, nevertheless it is to be understood that this invention encompasses the addition of complexes or compounds capable of decomposing to yield nitrogen at high temperatures into a rolling oil so that the nitrogen atmosphere will be formed in situ.

What is claimed is: I

1. In the process for the rolling of an aluminum alloy wherein said allow is passed through a plurality of cooperating rolls in order to reduce the thickness thereof, the improvement which comprises contacting said alloy with a rolling oil to which has been added gas substantially free from substances reactive with aluminum at the rolling temperature.

2. In the process for the rolling of an aluminum alloy wherein said alloy is passed through a plurality of cooperating rolls in order to reduce the thickness thereof, the improvement which comprises contacting said alloy with a mixture comprising water and a rolling oil to which has been added gas substantially free from substances reactive with aluminum at the rolling temperature.

3. The process of claim 2 wherein said gas is nitrogen.

4. In the process for the hot rolling of an aluminum alloy wherein said alloy is passed through a plurality of cooperating rolls in order to reduce the thickness thereof, the improvement which comprises releasing nitrogen within an aqueous emulsion of a rolling oil and thereafter spraying said emulsion onto said alloy as it enters and leaves the cooperating rolls so as to provide an inert atmosphere which substantially reduces the rapid formation of aluminum oxide.

5. In the process for the rolling of an aluminum alloy wherein said alloy is passed through a plurality of cooperating rolls in order to reduce the thickness thereof, the improvement which comprises contacting said alloy with an aqueous mixture containing 1-50 percent by weight of a rolling oil through which has been bubbled an inert gas in an amount ranging from about 5 to about 3000 cubic feet per hour at S.T.P. per 2400 cubic feet of said aqueous mixture, said gas being substantially free from substances reactive with aluminum at the rolling temperature.

6. The process of claim 5 wherein said gas is nitrogen.

7. In the process for the rolling of an aluminum alloy wherein said alloy is passed through a plurality of cooperating rolls in order to reduce the thickness thereof, the improvement which comprises contacting said alloy with an aqueous mixture containing 2-12 percent by weight of a rolling oil through which has been bubbled nitrogen in an amount ranging from about 25 to about cubic feet per hour at S.T.P. per 2400 cubic feet of said aqueous mixture.

8. The process of working an aluminum alloy while contacting it with an oil to which has been added gas substantially free from substances reactive with aluminum at the working temperature.

9. In the process for the working of an aluminum alloy in order to reduce the thickness thereof, the improvement which comprises contacting said alloy with an oil to which has been added gas substantially free from substances reactive with aluminum at the working temperature.

10. The process of claim 2 wherein said gas is selected from the group consisting of nitrogen, helium, hydrogen, neon, argon, krypton, and mixtures thereof.

References Cited by the Examiner UNITED STATES PATENTS 1,762,902 6/1930 Werder 252-15 2,337,008 12/1943 Vinther 7246 2,342,199 2/1944 Hurtt 252-9 2,617,769 11/1952 Nichols et a1 252-9 3,118,838 1/1964 Scherer 252--15 DANIEL E. WYMAN, Primary Examiner.

P. P. GARVIN, Assistant Examiner.

UNITED STATESPATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,301,029 January 31, 1967 Thomas L. Fritzlen et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, lines 5 and 6, cancel "doing business as Reynolds Metals Building,".

line 5, "as" should read at Signed and sealed this 22nd day of December 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer Column 1, 

1. IN THE PROCESS FOR THE ROLLING OF AN ALUMINUM ALLOY WHEREIN SAID ALLOW IS PASSED THROUGH A PLURALITY OF COOPERATING ROLLS IN ORDER TO REDUCE THE THICKNESS THEREOF, THE IMPROVEMENT WHICH COMPRISES CONTACTING SAID ALLOY WITH A ROLLING OIL TO WHICH HAS BEEN ADDED GAS SUBSTANTIALLY FREE FROM SUBSTANCES REACTIVE WITH ALUMINUM AT THE ROLLING TEMPERATURE. 